Digital driving method and system of OLED display device

ABSTRACT

The present disclosure provides a digital driving method and a digital driving system of an OLED display device. The digital driving method includes: dividing the frame into N sub frames, wherein N is an integer larger than or equal to 2, one of the sub frames is a full-brightness sub frame, the full-brightness sub frame includes a full-emission sub frame and the blanking period, pixels of the OLED display device keep emitting lights within the full-emission sub frame, and the blanking period follows the full-emission sub frame; determining the time ratios of driving the pixels in the sub frames as ½ N-1 , ½ N-2  . . . , 1 to increase the luminance of the OLED display device, wherein the time ratio of driving the pixels in the full-brightness sub frame is 1. By using the present disclosure, the brightness uniformity of the OLED display device can be increase.

RELATED APPLICATIONS

This application is a continuation application of PCT Patent ApplicationNo. PCT/CN2017/117736, filed on Dec. 21, 2017, which claims the prioritybenefit of Chinese Patent Application No. 201710679519.0, filed on Aug.10, 2017, which is herein incorporated by reference in its entirety.

FIELD OF THE DISCLOSURE

The disclosure relates to the display technology field, and moreparticularly to a digital driving method and a digital driving system ofan OLED display device.

BACKGROUND

The Organic Light Emitting Diode (OLED) display device hascharacteristics including self light-emitting, low driving voltage, highemitting efficiency, short response time, high resolution and contrast,about 180 vision angle, wide temperature range, great flexibility, imageimprinting for a larger panel size, etc. Thus, it is considered aprospecting display device.

Pixels of the OLED display device are arranged in a matrix, and a pixeldriving circuit can drive the OLEDs to emit lights. The driving methodof the OLED display device includes the analog driving method and thedigital driving method. When using analog driving method, TFTs ofdifferent pixels may have different characteristic parameters, sodifferent pixels may have different driving currents with the samedriving voltage, which causes the Mura (i.e. the bad brightnessuniformity of the OLED display device). By using the digital drivingmethod, the Mura can be reduced.

Referring to FIG. 1, a circuit diagram of a 3T1C pixel driving circuitof an OLED display device according to prior arts is shown. As shown inFIG. 1, the 3T1C pixel driving circuit includes a first TFT T1, a secondTFT T2, a third TFT T3, a storage capacitor Cst and an OLED D. Thesecond TFT T2 is a driving TFT. The gate of the second TFT T2 isconnected to a first node A, and the source of the second TFT T2 isconnected to a second node B. The first TFT T1 is configured to chargethe node A (i.e. the gate of the second TFT T2), and the third TFT T3 isconfigured to discharge the node A (i.e. the gate of the second TFT T2).

When the 3T1C pixel driving circuit drives the pixels of the OLEDdisplay device, the first TFT T1 charges the node A and the third TFT T3discharges the node A, so two Gamma voltages are outputted from the nodeA (i.e. the gate of the second TFT T2). These two Gamma voltages are themaximum Gamma voltage GM1 that leads the maximum brightness of the OLEDand the minimum Gamma voltage GM9 that leads the minimum brightness ofthe OLED. The current I flowing through the OLED can be calculatedaccording to the following equation.I=k(V _(GS) −V _(th))² =k(V _(A) −V _(B) −V _(th))²

In this equation, k is an eigen conductive factor of the second TFT T2,V_(GS) is the gate-source voltage of the second TFT T2, V_(th) is athreshold voltage of the second TFT T2, V_(A) is the voltage at the nodeA (i.e. the voltage at the gate of the second TFT T2), and V_(B) is thevoltage at the node B (i.e. the voltage at the source of the second TFTT2).

The variation ΔV_(th) of the threshold voltage V_(th) is smaller thanVA−VB because the element degradation or bad uniformity. Thus, comparedwith the analog driving method, the digital driving method can improvethe brightness uniformity of the OLED display device.

The first TFT T1 charges the node A and the third TFT T3 discharges thenode A, so two Gamma voltages are outputted from the node A. Thebrightness of the OLED display device is adjusted in a way similar tothe Pulse-Width Modulation (PWM) to have gray scales. Referring to FIG.2, a schematic diagram of light-emitting segments and blank segments ofeach of eight sub frames of each frame according to prior arts is shown.In FIG. 2, 8bits OLED display device is taken as an example. Each frameis sequentially divided into eight sub frames. The gray scale brightnesscan be determined by controlling the charging time and the dischargingtime of the sub frames. Thus, different sub frames can output differentgray scale, and digital driving signals are accordingly generated. InFIG. 2, the time ratios of driving the pixels in the sub frames (i.e.the first sub frame SF1 to the eighth sub frame SF8) are1/128:1/64:1/32:1/16:1/8:1/4:1/2:1. The eighth sub frame SF8 is afull-emission sub frame, and in the full-emission sub frame, pixels ofthe OLED display device keep emitting lights.

Generally speaking, each frame includes a driving period T_(D) and ablanking time T_(B). The driving period T_(D) is defined as the timeconsumed when scan lines in an effective display area are sequentiallydriven, and the blanking period T_(B) is defined as the time intervalbetween one driving period T_(D) and next driving period T_(D).Referring to FIG. 3, a schematic diagram of time segments of each ofeight sub frames of each frame according to prior arts is shown. Thedriving period T_(D) and a blanking time T_(B) are together divided intoeight sub frames. In other words, the driving period T_(D) is dividedinto eight segments and each segment belongs to one sub frame, and theblanking time T_(B) is also divided into eight segments and each segmentbelongs to one sub frame. Therefore, each frame is T_(D)/8+T_(B)/8. Inthe eight sub frames, the pixels do not emit lights near the blankingtime T_(B), and thus the pixels do not emit lights in the blanking timeT_(B). Referring to FIG. 4, another schematic diagram of light-emittingsegments and blank segments of each of eight sub frames of each frameaccording to prior arts is shown. In FIG. 4, the 8 bit gray scale istaken as an example. The time for the 255 gray-scale pixel having themaximum brightness to emit lights is about 25% of one frame. In otherwords, the maximum brightness generated by using the digital drivingmethod is only 25% of the maximum brightness generated by using theanalog driving method. Thus, the brightness of the OLED display deviceusing the digital driving method is pretty low.

SUMMARY

The present disclosure provides a digital driving method and a digitaldriving system of an OLED display device. The digital driving method andthe digital driving system can increase the brightness uniformity of theOLED display device.

The digital driving method provided by the present disclosure is adaptedto an OLED display device, and one frame of the OLED display deviceincludes a driving period and a blanking period. The digital drivingmethod includes: dividing the frame into N sub frames, wherein N is aninteger larger than or equal to 2, one of the sub frames is afull-brightness sub frame, the full-brightness sub frame includes afull-emission sub frame and the blanking period, pixels of the OLEDdisplay device keep emitting lights within the full-emission sub frame,and the blanking period follows the full-emission sub frame; determiningthe time ratios of driving the pixels in the sub frames as ½^(N-1),½^(N-2), . . . , 1 to increase the luminance of the OLED display device,wherein the time ratio of driving the pixels in the full-brightness subframe is 1.

In one embodiment of the digital driving method provided by the presentdisclosure, the driving period is divided by the full-emission sub frameand the (N−1) sub frames.

In one embodiment of the digital driving method provided by the presentdisclosure, N is 8.

In one embodiment of the digital driving method provided by the presentdisclosure, the time of driving the pixels from a first sub frame to aN^(th) sub frame gradually increases or gradually decreases.

In one embodiment of the digital driving method provided by the presentdisclosure, the OLED display device is an active OLED display device.

The digital driving system provided by the present disclosure is used inan OLED display device, and one frame of the OLED display deviceincludes a driving period and a blanking period. The digital drivingsystem includes a division module and a brightness setting module. Thedivision module divides the frame into N sub frames, wherein N is aninteger larger than or equal to 2. One of the sub frames is afull-brightness sub frame, and the full-brightness sub frame includes afull-emission sub frame and the blanking period. Pixels of the OLEDdisplay device keep emitting lights within the full-emission sub frame,and the blanking period follows the full-emission sub frame. Thebrightness setting module determines the time ratios of driving thepixels in the sub frames as ½^(N-1), ½^(N-2) . . . , 1 to increase theluminance of the OLED display device, and the time ratio of driving thepixels in the full-brightness sub frame is 1.

In one embodiment of the digital driving system provided by the presentdisclosure, the driving period is divided by the full-emission sub frameand the (N−1) sub frames.

In one embodiment of the digital driving system provided by the presentdisclosure, N is 8.

In one embodiment of the digital driving system provided by the presentdisclosure, the time of driving the pixels from a first sub frame to aN^(th) sub frame gradually increases or gradually decreases.

In one embodiment of the digital driving system provided by the presentdisclosure, the OLED display device is an active OLED display device.

According to the above descriptions, the digital driving methodincludes: dividing the frame into N sub frames, wherein N is an integerlarger than or equal to 2, one of the sub frames is a full-brightnesssub frame, the full-brightness sub frame includes a full-emission subframe and the blanking period, pixels of the OLED display device keepemitting lights within the full-emission sub frame, and the blankingperiod follows the full-emission sub frame; and determining the timeratios of driving the pixels in the sub frames as ½^(N-1), ½^(N-2) . . ., 1 to increase the luminance of the OLED display device, wherein thetime ratio of driving the pixels in the full-brightness sub frame is 1.Therefore, by using the digital driving method, a brightness decrease ofthe OLED display device can be improved so that the brightnessuniformity of the OLED display device will increase.

BRIEF DESCRIPTION OF THE DRAWINGS

Accompanying drawings are for providing further understanding ofembodiments of the disclosure. The drawings form a part of thedisclosure and are for illustrating the principle of the embodiments ofthe disclosure along with the literal description. Apparently, thedrawings in the description below are merely some embodiments of thedisclosure, a person skilled in the art can obtain other drawingsaccording to these drawings without creative efforts. In the figures:

FIG. 1 is a circuit diagram of a 3T1C pixel driving circuit of an OLEDdisplay device according to prior arts;

FIG. 2 is a schematic diagram of light-emitting segments and blanksegments of each of eight sub frames of each frame according to priorarts;

FIG. 3 is a schematic diagram of time segments of each of eight subframes of each frame according to prior arts;

FIG. 4 is another schematic diagram of light-emitting segments and blanksegments of each of eight sub frames of each frame according to priorarts;

FIG. 5 is a flow chart of a digital driving method of an OLED displaydevice according to an embodiment of the disclosure;

FIG. 6 is a schematic diagram of time segments of each of eight subframes of each frame according to an embodiment of the disclosure;

FIG. 7 is a schematic diagram of light-emitting segments and blanksegments of each of eight sub frames of each frame according to anembodiment of the disclosure; and

FIG. 8 is a block diagram of a digital driving system of an OLED displaydevice according to an embodiment of the disclosure.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The technical solutions in the embodiments of the disclosure will bedescribed dearly and completely hereinafter with reference to theaccompanying drawings in the embodiments of the disclosure so that thoseskilled in the art may better understand the solutions of thedisclosure. Evidently, the described embodiments are merely someembodiments rather than all embodiments of the disclosure. All otherembodiments obtained by persons of ordinary skill in the art based onthe embodiments of the disclosure without creative efforts shall belongto the protection scope of the disclosure.

It needs to be noted that the terms “first”, “second” and so on in thespecification, the claims and the accompanying drawings of thedisclosure are used for distinguishing similar objects, but are notnecessarily used for describing a specific sequence or a precedenceorder. It should be understood that data used in this way areinterchangeable in an appropriate condition, so that the embodimentsdescribed herein of the disclosure can be implemented in a sequencebesides those illustrated or described herein. In addition, the terms“include” and “have” and any other variants of them are intended tocover non-exclusive inclusion. For example, processes, methods, systems,products, or devices that include a series of steps or units are notnecessarily limited to the steps or units that are clearly listed, butmay also include other steps or units that are not clearly listed or areinherent in these processes, methods, products, or devices.

The present disclosure provides a digital driving method of an OrganicLight Emitting Diode (OLED) display device. One frame T of the OLEDdisplay device includes a driving period T_(D) and a blanking periodT_(B) (i.e. T=T_(D)+T_(B)). The driving period T_(D) is defined as thetime consumed when scan lines in an effective display area (i.e. the AAarea) are sequentially driven, and the blanking period T_(B) is definedas the time interval between one driving period T_(D) and next drivingperiod T_(D). In the blanking period T_(B), the OLED display deviceprocesses dummy pixels and some synchronous signals. Referring to FIG.5, a flow chart of a digital driving method of an OLED display deviceaccording to an embodiment of the disclosure is shown. As shown in FIG.5, the digital driving method of an OLED display device includesfollowing steps.

S110: dividing the frame into N sub frames, wherein N is an integerlarger than or equal to 2, one of the sub frames is a full-brightnesssub frame, the full-brightness sub frame includes a full-emission subframe and the blanking period, pixels of the OLED display device keepemitting lights within the full-emission sub frame, and the blankingperiod follows the full-emission sub frame.

FIG. 6 is a schematic diagram of time segments of each of eight subframes of each frame according to an embodiment of the disclosure, andFIG. 7 is a schematic diagram of light-emitting segments and blanksegments of each of eight sub frames of each frame according to anembodiment of the disclosure. As shown in FIG. 6 and FIG. 7, one frame Tof the OLED display device including a driving period T_(D) and ablanking period T_(B) is divided into N sub frames. N is an integerlarger than or equal to 2. For example, N can be 2, 3, 4, 5, 6, 7, 8 andthe like. In this embodiment, an 8 bit driving method is taken forexample, and thus N is 8 and one frame T of the OLED display deviceincluding a driving period T_(D) and a blanking period T_(B) is dividedinto eight sub frames, which are the first sub frame SF1, the second subframe SF2, . . . , and the eighth sub frame SF8. In these sub frames,the time for pixels of the OLED display device to emit lights (i.e. thetime of driving the pixels of the OLED display device) graduallyincreases. Especially, the last sub frame (i.e. the eighth sub frameSF8) is a full-brightness sub frame. As shown by the B area and the Darea in FIG. 6, the full-brightness sub frame includes the full-emissionsub frame and the blanking period T_(B). The blanking period T_(B)follows the full-emission sub frame, and pixels of the OLED displaydevice emit lights within both of the full-emission sub frame and theblanking period T_(B). The driving period T_(D) is evenly divided by thefirst sub frame SF1, the second sub frame SF2 . . . , the seventh subframe SF7 and the full-emission sub frame. In other words, the first subframe SF1, the second sub frame SF2 . . . , the seventh sub frame SF7and the full-emission sub frame are all T_(D)/8. In the first sub frameSF1, the second sub frame SF2, . . . , and the seventh sub frame SF7 areequal, but the full-brightness sub frame is larger than the first subframe SF1, the second sub frame SF2, . . . , and the seventh sub frameSF7 because the full-brightness sub frame includes the eighth sub frameSF8 and the blanking period T_(B).

S120: determining the time ratios of driving the pixels in the subframes as ½^(N-1), ½^(N-2) . . . , and 1 to increase the luminance ofthe OLED display device, wherein the time ratio of driving the pixels inthe full-brightness sub frame is 1.

As described, in the first sub frame SF1, the second sub frame SF2, . .. , and the eighth sub frame SF8, the time for pixels of the OLEDdisplay device to emit lights gradually increases. The time ratios ofdriving the pixels in the first sub frame SF1, the second sub frame SF2. . . , and the eighth sub frame SF8 are determined as ½^(N-1), ½^(N-2). . . , and 1. In the full-brightness sub frame, the time for pixels ofthe OLED display device to emit lights is T_(D)/8+T_(B). In the firstsub frame SF1, the time for pixels of the OLED display device to emitlights is ½⁷*(Td/8+T_(B)). In the second sub frame SF2, the time forpixels of the OLED display device to emit lights is ½⁶*(T/8+T_(B)). Inthe third sub frame SF3, the time for pixels of the OLED display deviceto emit lights is ½⁵*(T_(D)/8+T_(B)). In the fourth sub frame SF4, thetime for pixels of the OLED display device to emit lights is½⁴*(T_(D)/8+T_(B)). In the fifth sub frame SF5, the time for pixels ofthe OLED display device to emit lights is ½³*(T_(D)/8+T_(B)). In thesixth sub frame SF6, the time for pixels of the OLED display device toemit lights is ½² (T_(D)/8+T_(B)). In the seventh sub frame SF7, thetime for pixels of the OLED display device to emit lights is½¹*(T_(D)/8+T_(B)). In the eighth sub frame SF8, the time for pixels ofthe OLED display device to emit lights is ½¹*(T_(D)/8+T_(B)). In thisembodiment, the blanking period T_(B) is determined as 10% of the frameT for ease of illustration.

In this case, T_(B)=0.1T and T_(D)=0.9T.

Thus, in the full-brightness sub frame (i.e. SF8+T_(B)), the time forpixels of the OLED display device to emit lights is (0.9T/8+0.1T), whichis 1.7T/8. In a conventional driving method, in the last sub frame, timefor pixels of the OLED display device to emit lights is (0.9T/8+0.1T/8).Thus, compared with the conventional driving method, the digital drivingmethod provided by the present disclosure makes the time for pixels ofthe OLED display device to emit lights in the last sub frame be raised70% so that the brightness of the last sub frame is raised 70%.Likewise, in the present disclosure, the brightness of the other subframes can be raised at least 70%. Therefore, the overall brightness ofthe OLED display device can be raised 70%, such that a brightnessdecrease of the OLED display device can be improved and the brightnessuniformity of the OLED display device will increase.

In other embodiments, in the first sub frame SF1, the second sub frameSF2, . . . , and the eighth sub frame SF8, the time for pixels of theOLED display device to emit lights may gradually decreases. In otherwords, the time for pixels of the OLED display device to emit lights inthe first sub frame SF1>the time for pixels of the OLED display deviceto emit lights in the second sub frame SF8>the time for pixels of theOLED display device to emit lights in the second sub frame SF2>the timefor pixels of the OLED display device to emit lights in the third subframe SF3>the time for pixels of the OLED display device to emit lightsin the fourth sub frame SF4>the time for pixels of the OLED displaydevice to emit lights in the fifth sub frame SF5>the time for pixels ofthe OLED display device to emit lights in the sixth sub frame SF6>thetime for pixels of the OLED display device to emit lights in the seventhsub frame SF7>the time for pixels of the OLED display device to emitlights in the eighth sub frame SF8. In this case, the first sub frameSF1 is the full-brightness sub frame. In other words, the first subframe SF1 includes the full-emission sub frame and the blanking periodT_(B). Moreover, in other embodiments, the time for pixels of the OLEDdisplay device to emit lights may not gradually increases or graduallydecreases.

In this embodiment, the OLED display device is an active OLED displaydevice. The display circuit of the active OLED display device is a 3T1Cpixel driving circuit. The 3T1C pixel driving circuit can be referred toFIG. 1, and thus the relevant descriptions are omitted herein.

The present disclosure also provides a digital driving system of an OLEDdisplay device. One frame T of the OLED display device includes adriving period T_(D) and a blanking period T_(B) (i.e. T=T_(D)+T_(B)).Referring to FIG. 8, a block diagram of a digital driving system of anOLED display device according to an embodiment of the disclosure isshown.

As shown in FIG. 8, the digital driving system includes a divisionmodule 110 and a brightness setting module 120. The digital drivingsystem includes a division module and a brightness setting module. Thedivision module divides the frame into N sub frames, wherein N is aninteger larger than or equal to 2. One of the sub frames is afull-brightness sub frame, and the full-brightness sub frame includes afull-emission sub frame and the blanking period. Pixels of the OLEDdisplay device keep emitting lights within the full-emission sub frame,and the blanking period follows the full-emission sub frame. Thebrightness setting module determines the time ratios of driving thepixels in the sub frames as ½^(N-1), ½^(N-2) . . . , 1 to increase theluminance of the OLED display device, and the time ratio of driving thepixels in the full-brightness sub frame is 1.

In this embodiment, the driving period T_(D) is evenly divided by thefull-emission sub frame and the other (N−1) sub frames. From the firstsub frame to the N^(th) sub frame, the time for pixels of the OLEDdisplay device to emit lights may gradually increase or decrease. Inaddition, the OLED display device is an active OLED display device.Moreover, details about the digital driving system provided by thepresent disclosure can be referred to the descriptions relevant to thedigital driving method in the above embodiments, so the repeateddescriptions are omitted herein.

Each embodiment in this description is described in a progressivemanner, and in each embodiment, the differences between the embodimentand other embodiments are mainly explained; the same and similar partsof the various embodiments refer to each other. The system embodimentsare just simply described because they are substantially similar to themethod embodiments, and correlations there between just refer to onepart of descriptions of the method embodiments.

According to the above descriptions, the digital driving methodincludes: dividing the frame into N sub frames, wherein N is an integerlarger than or equal to 2, one of the sub frames is a full-brightnesssub frame, the full-brightness sub frame includes a full-emission subframe and the blanking period, pixels of the OLED display device keepemitting lights within the full-emission sub frame, and the blankingperiod follows the full-emission sub frame; and determining the timeratios of driving the pixels in the sub frames as ½^(N-1), ½^(N-2) . . ., and 1 to increase the luminance of the OLED display device, whereinthe time ratio of driving the pixels in the full-brightness sub frameis 1. Therefore, by using the digital driving method, a brightnessdecrease of the OLED display device can be improved so that thebrightness uniformity of the OLED display device will increase.

The foregoing contents are detailed description of the disclosure inconjunction with specific preferred embodiments and concrete embodimentsof the disclosure are not limited to these description. For the personskilled in the art of the disclosure, without departing from the conceptof the disclosure, simple deductions or substitutions can be made andshould be included in the protection scope of the application.

What is claimed is:
 1. A digital driving method, adapted to an OLEDdisplay device, wherein one frame of the OLED display device includes adriving period and a blanking period, comprising: dividing the frameinto N sub frames, wherein N is an integer larger than or equal to 2,one of the N sub frames is a full-brightness sub frame, thefull-brightness sub frame includes a full-emission sub frame and theblanking period, pixels of the OLED display device keep emitting lightswithin the full-emission sub frame, and the blanking period follows thefull-emission sub frame; applying N time ratios respectively indetermining driving periods for driving the pixels in the N sub frames,wherein values of the N time ratios are, respectively, ½^(N-1),½^(N-2, . . . ,) 1, each of the N time ratios is applied in determininga driving period for a corresponding one of the N sub frames, and a timeratio applied in determining the driving period for the full-brightnesssub frame is
 1. 2. The digital driving method according to claim 1,wherein the driving period is divided by the full-emission sub frame andthe (N-1) sub frames.
 3. The digital driving method according to claim1, wherein N is
 8. 4. The digital driving method according to claim 1,wherein time of driving the pixels from a first sub frame to a N^(th)sub frame gradually increases or gradually decreases.
 5. The digitaldriving method according to claim 1, wherein the OLED display device isan active OLED display device.
 6. A digital driving system of an OLEDdisplay device, wherein one frame of the OLED display device includes adriving period and a blanking period, comprising: a division, dividingthe frame into N sub frames, wherein N is an integer larger than orequal to 2, one of the N sub frames is a full-brightness sub frame, thefull-brightness sub frame includes a full-emission sub frame and theblanking period, pixels of the OLED display device keep emitting lightswithin the full-emission sub frame, and the blanking period follows thefull-emission sub frame; and a brightness setting module, applying Ntime ratios respectively in determining driving periods for driving thepixels in the N sub frames, wherein values of the N time ratios are,respectively, ½^(N-1), ½^(N-2, . . . ,) 1, each of the N time ratios isapplied in determining a driving period for a corresponding one of the Nsub frames, and a time ratio applied in determining the driving periodfor the full-brightness sub frame is
 1. 7. The digital driving systemaccording to claim 6, wherein the driving period is divided by thefull-emission sub frame and the (N-1) sub frames.
 8. The digital drivingsystem according to claim 6, wherein N is
 8. 9. The digital drivingsystem according to claim 6, wherein time of driving the pixels from afirst sub frame to a N^(th) sub frame gradually increases or graduallydecreases.
 10. The digital driving system according to claim 6, whereinthe OLED display device is an active OLED display device.